|fahnen/7.jpg Satellite Beacons|
This script from the Houston AMSAT Net was written by AMSAT Area Coordinator Bruce Paige, KK5DO. Authorization is given for the use of this information over any ham band. Please give credit for the script where credit is due.
Here is a look at beacons. Beacons come in many different flavors and I will cover several of them here. There are becons that have data that requires a decoding program to use them. There are others that give their data in CW.
I guess the easiest thing we can discuss is what the beacons do and how to use them. First, a beacon provides us with a gauge to determine how much power we should use. If you transmit your signal and compare it to the beacon strength, you can then adjust your power up or down to match the beacon. That would be the optimum transmitting power for your station. The next thing that the beacons provide us with is a schedule of the satellite's activity. It might tell you that it is on during a particular time period and off during others.
The beacon can also help us tune our radio to compensate for doppler shift. Since we know the beacon is supposed to be on a certain frequency, we can calculate where our signal will be based on the current reception of the beacon.
Let's look at the beacon or we'll call it telemetry for Dove 17. Dove only sends data with an occasional synthesized voice transmission. When it is transmitting data, it can be received using standard FM 1200 baud packet.
You will receive power supply information, temperature, its location in the sky, status of the on-board computer and other things that I am not even sure of. As I mentioned earlier, this beacon requires a 1200 baud FM packet to listen to it. Tune to 145.825 MHz.
On to AO-13 one of the high orbit satellites. The beacon is USB. At 0 and 30 minutes past the hour the beacon transmits about 5 minutes of 10 wpm CW. At 15 and 45 minutes past the hour, the beacon transmits RTTY for 5 minutes. All other times are used to transmit the PSK engineering data and telemetry. The RTTY is at 50 baud however most 45 baud machines will be able to copy it.
Some of the things that you can get from the CW beacon is the mode the satellite will be in at which phase counts, keplerian data and other general announcements. The RTTY bulletins contain the same data as the CW plus satellite status telemetry.
Most of the satellites have a beacon. They are normally at the top or bottom end of the frequency spread for that satellite. Some have two beacons. AO-13 has a beacon at 145.812 and 145.985. AO-10 has two beacons, one at 145.987 and one at 145.810.
RS-10 has a beacon at 29.357 and 29.403 both CW. FO-20 has a beacon at 435.795.
There are many more beacons, If you are interested in more, you can get a frequency guide from Martha at AMSAT headquarters.
There is a publication that you can also get from Martha which explains how to decode some of the beacons. The title is "Decoding Telemetry from the Amateur Satellites". It would be a good publication if you are interested in snooping at the various numbers that appear in the beacon listings.
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